The invention relates to an impregnated compound metal as a contact material for vacuum switches, comprising a sintered metal matrix impregnated by an impregnating metal or impregnating metal alloy, the melting point of said matrix being higher than that of the impregnating substance.
Contact materials for vacuum switches whose field of application should also cover the area of higher capacities, must meet as basic conditions the requirements of high current breaking ability (&gt; 10kA) and good dielectric strength (&gt; 12kV). At the same time, such materials must have a long service life, i.e., they must burn off little and their welding forces must be adequately low (&lt; 800 N). Pure alloys based on copper or sintered impregnated materials have been used as contact materials. These sintered impregnated materials consist of a sintered porous metal matrix of high melting point which is impregnated by a metal or metal alloy of lower melting point and better electric conductivity, forming a so-called impregnated compound metal. While the contact materials mentioned do meet the requirements of an adequately long service life and high breaking current, they do not satisfy the requirements of a sufficiently low welding force. It has heretofore been attempted to admix bismuth or tellurium to the said alloys on the basis of copper or to the sintered impregnated materials as ingredients lowering the welding force. But due to their low melting points (&lt; 2000.degree. C), bismuth and tellurium develop very high vapor pressures, thereby reducing the quenching ability of the switch and, hence, its current breaking capability in an impermissible manner.